Fire resistant acrylonitrile polymer articles containing submicron antimony oxide particles

ABSTRACT

1. AN ACRYLONITRILE POLYMER FIBER CONTAINING AN AVERAGE OF AT LEAST ABOUT 50% ACRYLONITRILE IN THE POLYMER MOLECULE AND UP TO 50% BY WEIGHT OF A HALOGEN CONTAINING MATERIAL KNOWN TO IMPACT FIRE RESISTANCE TO POLYACRYLONITRILE ARTICLES, AND FURTHER CONTAINING ANTIMONY OXIDE PARTICLES IN AN AMOUNT OF FROM 1% TO 20% BY WEIGHT OF THE TOTAL WEIGHT OF SAID FIBER, CHARACTERIZED IN THAT SAID ANTIMONY OXIDE HAS AN AVERAGE PARTICLE DIAMETER RANGING FROM ABOUT 100 A. TO ABOUT 300 A., WHEREBY A LUSTRE INDEX OF SAID FIBER ABOVE 30% IS OBTAINED.

91,573, Nov. 20, 1970, now Patent No. 3,743,708. This 1 application Feb.12, 1973, Ser. No. 331,409

Int. Cl. C08f 45/56, 45/58 US. Cl. 260-45.75 B 3 Claims ABSTRACT OF THEDISCLOSURE Polyacrylonitrile fiber having up to 50% by weight of ahalogen containing material 'known to impart fire resistance topolyacrylonitriles and further containing particulate antimony oxide isimproved in luster by the use of submicron antimony oxide having averageparticle diameter of from about 100 A to about 300 A.

This application is a continuation-in-part application based on US.patent application Ser. No. 91,573, filed Nov. 20, 1970, now issued asUS. Pat. No. 3,743,708.

The present invention relates to articles prepared according to theteachings of said application, Ser. No. 91,573, in that it is concernedwith fire-resistant or selfextinguishing compositions in whichparticulate antimony oxide is used as a flame retardant additive fortextiles and plastics. In particular, the present invention relates tolustrious polyacrylonitrile fibers containing submicron antimony oxide.

As used herein, the term acrylonitrile polymer means a composition ofmatter which contains an average of at least about 50% acrylonitrile inthe polymer molecule. The remainder of the polymer molecule may containup to about 50% of other ethylenically unsaturated materials such asvinyl and/or vinylidene chloride as is well known in the art.Illustrative of compounds, which may be copolymerized with acrylonitrileto form polymers useful for the practice of this invention, are thosefound polymers at the present time is in the form of fibers. Such.fibers may be used as continuous filaments or as staple fibers in theproduction of knitted fabrics, woven fabrics,

non-woven felts, pile fabrics, carpets, etc.

For many uses, it is important that the shaped articles, especiallyfibers, of acrylonitrile polymers be made fireresistant orself-extinguishing when exposed to flame. It

has been known thas this result could be obtained by the use of certainadditives and/or the ethylenically unsaturated materials which can becopolymerized with the acrylonitrile. Such additives or materials usefulin the present invention have nuclear substitution of halogen groupssuch as chlorine and bromine.

The combination of antimony oxide as an additive to synergize the flameretardency property of these halogen substituted additives and tocopolymerize monomers with ethylenically unsaturated monomers is wellknown. US. Pat. 3,331,797 teaches of chloroparaffins as well as with awide variety of nuclear substituted brominated aromatic compounds inconjunction with antimony trioxide. Co-pending US. patent application,Ser. No. 91,573, filed Nov. 20, 1970, discusses particulate antimonyoxide in combination with brominated and/or chlorinated aromatics forfire retardancy of polyacrylonitriles. Such particulate antimony oxide,however, delusters the fibers and reduces their attractiveness incommerce.

United States Patent ICO 0 tives and monomers for commercial utilizationin polyacrylonitrile fibers as well as the polyolefine compositions suchas taught in US. Pat. No. 3,331,797. Such polyolefines are polyethylene,polypropylene, polyisobutylene and the solid mixed polymers of thecorresponding monomers. The polyolefines may contain the usual additionsof fillers, colors, lubricants, and/ or stabilizers.

The expression flame-resistant as employed herein, means a materialwhich imparts resistance to afterflarne after being ignited in an openflame and then removed from the flame.

The preparation of the antimony oxide in submicron particle size isfully set forth in said application, Ser. No. 91,573, filed Nov. 20,1970, now US. Pat. No. 3,743,708. Briefly, the submicron antimony oxideparticles have been produced by the steps of: introducing a feed ofantimony and/ or antimony oxide into a plasma or tail flame thereof;vaporizing said feed in said plasma including the tail flame portionthereof; admixing a secondary gas into said tail flame in an amount toprovide less than 0.01 grams of said vaporized feed per liter of admixedgas and plasma as a controlled quench to cool rapidly the antimonyoxide; and, adjusting the oxidizing component of said secondary gas asrequired to assure complete oxidation of said antimony oxide. Theprecipitated oxide can be collected by filtration through a filterranging in particle average diameter of A to 300 A.

The submicron oxide can then be added to the polymer dope solution as adry powder or as a colloidal suspension in water. The suspension can beproduced by conventional means such as a colloid mill. A dispersingagent can be usefully added to the colloidal suspension.

Polyacrylonitrile and many of the fiber and filmforming copolymers ofacrylonitrile are advantageously fabricated by a wet-spinning processwherein the polymer composition is extruded from compositions of thepolymer in polyacrylonitrile dissolving solvents, particularly aqueoussolutions of sodium thiocyanate.

The additive and antimony oxide must be uniformly dispersed in thepolymer solution or spin dope. Such may be produced by dissolving theadditive in the spin dope or polymer solution if such additive issoluble therein or may be produced by any of the mechanical techniquesfor dispersing insoluble liquids or solids when the additive compound isinsoluble in the polymer solution or spin dope. The technology ofproducing the uniform dispersion of additive and antimony oxide will notbe described in detail herein since such techniques are well known inthe art and are used for dispersing materials, such as titanium dioxidedelusterants, dyes, pigments, etc., in polymer solutions and spin dopes.

The amounts of the halogen containing fire retardant additive or monomerpresent in the acrylonitrile polymer to be protected cannot be set forthcategorically with specific numerical ranges since different amounts offireretardancy or self-extinguishing characteristics may be needed fordifferent uses to which the acrylonitrile polymer articles may be put aswell as due to (a) the differences in halogen contents of the variousbrominated and/or chlorinated additives or monomers which are useful,(b) the relative higher effectiveness of bromine compounds as comparedwith corresponding chlorine compounds, (c) the varying synergism of theantimony oxide with the many additives, and (d) the desired degree offlame-retardancy to be achieved. However, using the principles of thepresent invention, and known tests such as ASTMD 2863-70, one canreadily determine the optimum concentrations of compounds in thissynergistic mixture which should be used for any given application toachieve satisfactory effective fire-resistant or self-extinguishingcharacteristics and still retain the useful luster index of thepolyacrylonitrile fiber.

For purposes of this disclosure, a luster index of 30% is established asthe boundary between commercial utility and non-utility, i.e., valuesbelow 30% lack requisite luster. Luster index is obtained by acomparison of several reflectivities of fiber wound into yarn.

In determining the decrease in luster several measure ments of the fiberreflectance are made in order to establish a luster index. The lusterindex is determined by reflectance recorded with a Hunterlab D-16Glossmeter. The test provides a quantitative measurement of fiber lusterthat correlates with visual assessment of luster. The fiber samples areprepared for test by wrapping yarn about a cardboard. Light reflectedfrom the surface of the yarn sample is viewed and measured in the +60(specular) and the +20 (diffuse) direction. Luster in percent is equalto l: diffuse reading specular reading Although known at least in partin the art, it may be useful to detail representative additives andmonomers which provide fire resistance.

U.S. 2,669,521 describes the use of chlorinated hydrocarbons,particularly chlorinated paraflin wax in combination with an inorganicoxide, preferably antimony oxide, and tricresyl phosphate as a flameproofing mixture for polymeric thermoplastic materials.

US. 3,271,343 describes polyacrylonitriles flame retardend withpolyepihalohydrins.

Another approach appears in US. Pat. 3,697,218 wherein thepolyacrylonitrile has as one constituent thereof a polymerizedethylenically unsaturated glycidyl compound the epoxy group of which isreacted with a bromine, chlorine or phosphorous containing compound.

It is also known that the halogen content of halogenated organiccompounds often has an effect of reducing the flammability both of thecompound containing the halogen and of flammable organic materialsintimately admixed therewith.

Other suitable additives include: nucleus halogenated diaromaticcompounds halogenation products of dibenzyl, dimethylbenzyl,diethylbenzyl, benzyltoluene, dibenzyltoluene,benzylmethylbenzylbenzene, diphenylpropane, diphenyls and theirmixtures; diaromatic or aromatic-aliphatic ethers containing at leastthree nucleus substituted bromine atoms; 2,4,6 tirboromanilines;hexabromobenzene; bispentabromophenyl ether; hexachlorobenzene;pentachlorophenol; pentabromophenol; pentabromomonochlorobenzene;1,4,5,8 tetrabromonaphthalene; hexabromonaphthalenes; and,octachloronaphthalene.

As the instant invention herein relates essentially to the uniqueadvantage in using submicron sized antimony oxide, it appearsunnecessary to further apply known fireretardant polyacrylonitriletechnology.

The disadvantages of the prior art relating to the use of Sb O or Sb Ohave been overcome by the preparation of an acrylonitrile polymer fibercontaining an average of at least about 50% acrylonitrile in the polymermolecule and up to 50% by weight of a halogen containing material knownto impart fire-resistance to acrylonitrile articles, and furthercontaining antimony oxide particles in an amount of up to 20% by weightof the total weight of said fiber, characterized in that said antimonyoxide has an average particle diameter ranging from about 100 A. toabout 300 A., whereby a lustre index of said fiber above 30% isobtained.

1 times 100.

In its preferred embodiment the antimony oxide content of said fiberranges from about 1 to about 10 percent by weight of the total fiber.

For a clearer and more detailed description of this invention asembodied in specific examples thereof, reference may be made to thefollowing examples which are presented for illustrative purposes only.In these examples, all parts and percentages are by weight unlessotherwise noted.

EXAMPLE 1 A flow of 0.58 g./min. of 325 mesh antimony powder issuspended in a stream of 0.8 1./min. of argon carrier gas and introducedinto the radio frequency plasma through a downstream facing probepositioned in the plasma. The plasma-forming gas is argon and its flowis 1.2 s.c.f.m. The power coupled to the plasma discharge is 1.35 kw.resulting in a power density of 565 B.t.u./lb. argon. Into the plasmatail flame 10 s.c.f.m. of oxygen quench gas is admixed. White antimonyoxide product, collected by passage of the gas stream through a heatexchanger and through a filter bag, was obtained in 91% yield. Theantimony oxide product had a surface area average particle diameter of340 A.

EXAMPLE 2 A flow of 0.43 g./min. of 0.15-0.2 antimony oxide powder(Harshaw Chemical Co.) is suspended in a stream of 1.2 L/min. of oxygencarrier gas and introduced into the plasma. The plasma forming gas isargon and its flow is 1.2 s.c.f.m. The power coupled to the plasma is1.35 kw., resulting in a power density of 560 B.t.u./lb. argon. Into theplasma tail flame 10.3 s.c.f.m. of air was admixed. White antimony oxidewas collected as above and at substantially yield. The antimony oxidecollected had an average particle diameter of 142 A.

EXAMPLE 3 A high intensity are is maintained between a 1 in. diameteranode, comprised of a mixture of antimony oxide and graphite and a /2in. diameter thoriated tungsten cathode. The cathode is constructed bycompressing a mixture of 75 parts of mesh antimony oxide with 22 partsof graphite and a suitable binder. The are current is 450 amps and theelectrode vaporization rate is 1.3 lb./hr. The electrodes are situatedin a closed chamber whereby an air quench line was incorporated alongwith the electrodes. Air quench gas at a rate of 3 s.c.f.m. is injectedinto the tail flame at an angle of 45 from the anode axis and 1 /2 in.from the anode. The gas flow from the arc chamber passes through aconnecting heat exchanger at the outlet of which is a filter bag forcollection of the Sb O The exit gas passes through the filter bag to anexhaust duct. The Sb O product is collected in substantially 100% yieldand has a surface area average particle diameter of A. In addition to SbO the solids product collected contained 0.12 weight percent carbon.

EXAMPLE 4 Antimony oxide made by the process of Example 2 was tested asa nondelustering fire retardant additive in acrylic fiber. The antimonyoxide was mixed by colloidal mill in a spin dope of acrylonitrilepolymer (89.3% acrylonitrile- 10.7% methyl methacrylate) dissolved in asolvent for the polymer (50 parts sodium thiocyanate50 parts water) toproduce a uniform fine dispersion thereof. Thereafter, the spin dope wasfiltered, extruded through spinnerette orifices, coagulated (using a 12%aqueous sodium thiocyanate solution at 3 C. as coagulant), washed freeof solvent, dried, and relaxed at 130 C. in a water-steam environment toprepare fibers by a known process.

The fiber contained 3% by weight of various sized antimony oxideparticles as the sole additive. Luster index measurements were made onthe fiber and are shown below. An acceptable luster index (indicative ofthe brightness of the fiber) is 30%.

As the particle size of Sb O was decreased, acceptable luster indiceswere obtained.

EXAMPLE 5 Instead of admixing the antimony oxide as a powder, thisExample features its incorporation into polyacrylonitrile dope solutionas a colloidal suspension. The colloidal suspension is Sb O in waterwith stibnic acid dissolved therein. The colloidal suspension, having anaverage particle diameter of about 150 A., can be obtained from NyanzaCorp. of Ashland, Mass. The colloidal suspension was progressivelydiluted with sodium thiocyanate solutions of increasing sodiumthiocyanate concentration until a stable system having a concentrationof about 43% by weight sodium thiocyanate with about 5% Sb O wasobtained. An appropriate amount of this antimony oxidesuspension in asodium thiocyanate solution was in-line mixed with a polyacrylonitrile(89.3% of acrylonitrile and 10.7% of methylmethacrylate) dope solutionof 11.2% polymer, 40.5% sodium thiocyanate and 48.3% water to obtainvariations of antimony content in the fiber. The uniformly mixed polymerdope solution was then immediately spun and processed into fiber asabove. The results were as follows:

Commercially available grade antimony oxide.

The data of Tables I and II show the lustrous character ofpolyacrylonitrile fibers containing synergistically useful amounts ofantimony oxide. Amounts of antimony oxide up to 20% by weight of thefiber can be usefully 6 EXAMPLE 6 The flame retardancy ofpolyacrylonitrile fibers containing antimony oxide is shown in thefollowing test. Polyacrylonitrile (81.1% acrylonitrile, 9.7% vinylchloride and 9.2% methylmethacrylate) fibers containing 4.0%hexabromobenzene and 2.7% Sb O of 150 A. average particle diameter sizewere evaluated for fiame-retardancy relative to polyacrylonitrile fibers(same polymer content) not containing the hexabromobenzene and Sb Oaccording to ASTM Procedure D 2863-70. In each instance the test samplehad a weight of 4.5 oz./yd. of fiber of yarn having 18 singles cottoncount of 2.5 denier per filament fiber. The L.O.I. for thehexabrom0benzene-Sb O containing fabric was 25 as compared to thecontrol value of 21 indicating significant fire retardancy of the fabriccontaining hexabromobenzene and Sb O The limiting oxygen index (L.O.I.)is defined as follows:

The minimum oxygen percent in a non-combustible gas required to supportcombustion of plain jersey knit having a density of 4.5 ounces persquare yard prepared from an eighteen singles yarn of the fiber undertest.

What is claimed is:

1. An acrylonitrile polymer fiber containing an average of at leastabout 50% acrylonitrile in the polymer molecule and up to 50% by weightof a halogen containing material known to impart fire resistance topolyacrylonitrile articles, and further containing antimony oxideparticles in an amount of from 1% to 20% by weight of the total weightof said fiber, characterized in that said antimony oxide has an averageparticle diameter ranging from about A. to about 300 A., whereby alustre index of said fiber above 30% is obtained.

2. The article of claim 1, wherein said antimony oxide content rangesfrom about 2 to about 10% by weight of the total fiber.

3. An acrylic fiber having about 3% by weight, based on said fiber, ofsubmicron antimony oxide particles, said particles having an averagediameter ranging about 100 A. to about 208 A.

References Cited UNITED STATES PATENTS 3,560,441 2/1971 Schwarcy et a1.260-45.75 3,449,072 6/ 1969 Freeman 106-288 3,480,582 11/1969 Brooks260-45.75

V. HOKE, Primary Examiner US. Cl. X.R.

260-41 B, 45.75 R, 45.9, 45.95 G

1. AN ACRYLONITRILE POLYMER FIBER CONTAINING AN AVERAGE OF AT LEASTABOUT 50% ACRYLONITRILE IN THE POLYMER MOLECULE AND UP TO 50% BY WEIGHTOF A HALOGEN CONTAINING MATERIAL KNOWN TO IMPACT FIRE RESISTANCE TOPOLYACRYLONITRILE ARTICLES, AND FURTHER CONTAINING ANTIMONY OXIDEPARTICLES IN AN AMOUNT OF FROM 1% TO 20% BY WEIGHT OF THE TOTAL WEIGHTOF SAID FIBER, CHARACTERIZED IN THAT SAID ANTIMONY OXIDE HAS AN AVERAGEPARTICLE DIAMETER RANGING FROM ABOUT 100 A. TO ABOUT 300 A., WHEREBY ALUSTRE INDEX OF SAID FIBER ABOVE 30% IS OBTAINED.